A simple solar radiation model for computing direct and diffuse spectral fluxes / Robert B. Giorgis.

Tese (Ph.D.) - University of California, 1975

A solar spectral model which describes the solar radiation flux on a clear day at any given location is developed and tested. The model computes spectral fluxes of global, global photon, direct, and diffuse, solar radiation incident at the surface. Input parameters describe location and atmospheric characteristics. Characteristics which describe a location include latitude, altitude, slope orientation, and surface albedo. Atmospheric characteristics described are turbidity, precipitable water vapor, and total ozone content. The model was constructed using a one-layer, homogeneous atmosphere and is patterned after models described by Robinson (1966) and Leighton (1961). Refinements include: 1. Use of climatological data to predict the total ozone content, if it is not known. 2. A more advanced treatment of infrared solar radiation (0.8-4.5 microns) absorption. 3. A more complex scheme for predicting diffuse radiation. 4. The capability of handling a spectral albedo. 5. Inclusion of albedo dependence on zenith angle. Input parameters to the model are minimized and several simplifying features are incorporated for ease of handling variables not routinely measured. Turbidity and total ozone content are treated as climatological estimates if specific location measurements are not available. Precipitable warwe vapor can be predicted using surface vapor pressure, since the sounding network is not dense. These features allow for use of the model by researchers outside the field of solar radiation. Since complete measurements with needed location and atmospheric characteristics could not be found, the validity of the model was tested by comparison with a more complex, multilayered atmosphere model by Dave, Halpern, and Braslau (1975). With appropriate adjustment for differences in extraterrestrial solar radiation fluxes, calculated fluxes of total direct, diffuse, and global, radiation from the model presented were 11.5, 20.1, and 13.2 percent lower, respectively. Direct spectral fluxes exhibited close agreement in their spectral compositions, with slight exception in the 0.8 to 0.95 micron region. Diffuse spectral fluxes were slightly high in the ultraviolet region and lower in the rest of the spectrum as compared to the multilayered atmosphere model. A sensitivity analysis of the model was also conducted, and the most influential inputs were found to be latitude, slope orientation, and turbidity, while the least influential was total ozone content. .